1. Field of the invention
The present invention relates to a system and method for transmitting image data on a telephone network or equivalent. More specifically, the present invention relates to a novel transmission control procedure which is suitable for sending and receiving image data of relatively small data amount through the telephone network or equivalent as a video or visual telephone system.
2. Description of the prior art
Conventionally, a facsimile communication system is well known as a system for sending and receiving the image data through a telephone network or equivalent. The facsimile communication system is adapted to transmit the image data through a transmission control procedure including phases A-E as shown in FIG. 1 in accordance with the T series recommendation of CCITT. The phase A is a phase for setting call up, the phase B is a pre-message phase, and the image data is transmitted in the phase C. The phase D is a post-message phase and the phase E is a phase for putting call down.
In the conventional transmission control procedure of the facsimile communication system, time periods required for the phases A, B, D and E are respectively approximate 3 seconds, 8 seconds, 2.5 seconds and 1 second in spite of a length of the image data. Therefore, when the data amount of the image data is small, time period which does not take part in transmission of the image data is relatively increased, thus there is a problem that a transmission efficiency becomes worse. Specially, in the video or visual telephone system in which a still picture or image is transmitted rather than a moving picture or image, the image data to be transmitted is only for one image screen, and therefore, if a complex transmission control procedure as in the conventional facsimile communication system is applied, the transmission efficiency is very bad.